Magneto



w. DRN

Jan. 3, 1939.

MAGNETO Filed Feb. 20, 1937 2 Sheets-Sheet l Jan. 3, 1939.

w. lDQRN 2,142,094

MAGNETO Filed Feb. 20, 1937 2 Sheets-Sheet 2 y INVENTOR. l/l/a /e f-00./77

A TTORNE Y.

Patented Jan. 3, 1939 2,142,094 MAGNEro vWalter Dorn, Stuttgart.Germany, assgnor to Robert Bosch Gesellschaft mit beschrnkter Haftung,Stuttgart, Germany Application February 20, 1937, Serial No. 126,819 InGermany March 9, 1936 4 Claims.

This invention relates to' magneto electric generators -and moreparticularly to a magneto for supplying ignition sparks to an internalcombustion engine.

In prior magnetos it has been necessary to provide an interrupter whichperiodically interrupts the circuit of the primary winding. 'I'he suddencessation of current flow therein causes the collapse of the magneticfield produced thereby, which simultaneous with a reversal or reductionof the ux produced by the permanent magnet of the magneto, induced asparking voltage in the associated secondary winding. In the inventionto be described herein, no interrupter is required, and the necessity ofadjustments in compensating for the wear occurring in parts thereof iseliminated, as well as the initial expense of the interrupter mechanism.Additionally, the present invention discloses a magneto which has aquicker time ratechange of ux in the magnetic circuit and in consequenceis more emcient in the generation of sparking voltages at low speeds.The prior art magnetos were relatively ineilicient at low speed andsometimes required -additional special apparatus, such as impulsecouplings, to achieve satisfactory ignition performance during thestarting period of the engine.

One of the objects of this invention is, therefore, to provide a noveland improved magneto which is more economical in construction andeilcient in operation.

Another object is to provide a magneto which is more eiiicient at lowrotational speeds.

Still another object is to provide an improved magneto which requires noassociated interrupter mechanism.v

A further object is to provide a magneto having a novel and improvedmagnetic circuit therein.

Other objects and advantages will in part be specifically stated and inpart be obvious when the following specification is read in connectionwith the drawings,l in which:

Fig, 1 is a schematic showing of the improved magneto, which has arotating permanent magnet; Fig. 2 is a diagrammatic showing of thevariations of magnetomotive force occurring during a full rotation ofthe rotor; Fig. 3 is a diagram showing the hysteresis loop of the coilcore member; Fig. 4 is an enlarged cross section showing the preferredform of the coil core; and Fig. 5

is an enlarged cross section of an alternative construction of the coilcore.

Referring now in more detail to Fig. 1, the reference numeral Iindicates a rotatable permanent magnet preferably of high'coerciveforce. Adjacent the magnet are the pole faces 2 of the polepieces 3, andrmly secured between the upper extremities of the polepieces is a coilcore l, carrying a primary winding 5 and a secondary winding 6. Securedto each polepiece 3 and extending inwardly below the coil are threadedstud bolts l. A turnbuckle member 8 is internally threaded tocol-operate with the threads of the respective stud bolts 'igso as to becapable of applying force thereto, forl a reason later to be explainedin detail. A frame 9 receives the lower ends of the polepieces 3 andmaintains the gap between the rotor magnet 'ii and polefaces 2 at aconstant value, regardless of any adjustment of the turnbuckle 8.

Fig. 2 shows the change in ileld intensity or magnetomotive forcev H,during a full rotation of the rotary magnet I; with the position asshown in Fig. 1 corresponding to position 0 thereof.

The coil core 4 is composed of an alloy having the hysteresis loop shownin Fig. 3, for instance a nickel-iron alloy which contains about 8%nickel and which is held under a mechanical tension of at least 6000kilograms per square centimeter, as described in the book of Millier-Pouillet, Vol. 4, part 4 at page 146, entitled Lehr- -buch der Physikund Meteorlogie, 10th edition,

"tive force hasy been reduced through zero, and

then reversing, has risen in the opposite sense to a critical value.Thereupon the reversal of flux occurs abruptly in the alloy and the fluxassumes substantially 80% of its full value almost instantaneously. Thisis shown in Fig. 3 where H represents magnetomotive force and Brepresents the value of the ilux lines per square centimeter. Thehysteresis loop there shown has a right angle in each phase whichillustrates the quick time rate of change of iiux never before availablein a magneto.

The coil core l is composed of an alloy of the foregoing nature, andwhile it may be of laminatons, the preferred form is a single sheetwhich is folded upon itself as shown in Fig. 4, or is alternativelyrolled into cylindrical form as shown in Fig. 5. The stud bolts 1 areforced apart by the turnbuckle member 8 in order to place the coil core4 under the proper longitudinal tension.

It will be obvious that many modications and changes may be made byanyone skilled in the art without departing from the spirit and scope ofthe invention as set forth in the following claims.

Having described the invention, claimed is: l

1. In a magneto having a rotor, a current generating coil, a metalliccore for said coil, pole pieces attached to each end of said core, meansfor forcing said polepieces apart, whereby said core is placed undertension, and means preventing displacement of the portion of the polepieces adjacent said rotor.

2. In a magneto having a rotor, a current generating coil, a metalliccore for said coil, pole pieces attached to each end of said core, astud bolt secured to each pole piece, means engaging what is said studbolts for forcing said pole pieces apart, whereby said core is placedunder tension, and means preventing displacement of the portion of thepole pieces adjacent said rotor.

3. In a magneto, a current generating coil, a metallic core for saidcoil, a polepiece attached to each end of said core, a stud bolt securedto each polepiece, means engaging said stud bolts for forcing saidpolepieces apart, and a frame member securing said polepieces at a pointremote from said core, whereby said core may be placed under tension.

4. In amagneto, a current generating coil, a metallic core for saidcoil, a polepiece attached to each end of said core, a stud bolt securedto each polepiece, a turnbuckle member engaging said 'stud bolts forforcing said polepieces apart, and a frame member securing saidpolepieces at a point remote from said core, whereby said core may beplaced under tension.

WALTER DORN.

